534 



STUDIES FOR STUDENTS 



TABLE III 



MODULUS OF ELASTICITY 



In Pounds per Square Inch 



Granite and rhyolite : twenty-one samples from 

 eleven different quarries 



Limestone : eleven samples from five different 

 quarries 



Sandstone : twenty-eight samples from ten dif- 

 ferent quarries 



Highest test 



2,070,000 



1,835,700 



400,800 



156,000 

 3L500 

 32,000 



Average 



1,068,634 

 786,145 

 163,861 



HARDNESS 



The hardness of a stone can be easily determined with the 

 abrading machine known as the Deval. 1 For making this test a 

 definite quantity (5 kg) of cubical pieces of stone from two to 

 two and one half inches in diameter are placed in one of the 

 cylinders of this machine, which is then rotated for five hours at 

 a rate of about thirty-three revolutions per minute. The per- 

 centage of dust which is worn off by this treatment is the meas- 

 ure of the hardness of the stone. The coefficient of wear, which 

 is another and the usual method of expressing the hardness, is 

 computed from the following formula : 



20X20 



W 



in which 



Q =the coefficient of wear 

 ^K^the quantity of dust formed. 



Two samples of granite from each of two quarries were 



tested in the abrading machine, with the results given in Table 



IV. Quartzite from one quarry, trap rock from one quarry, and 



limestone from seven quarries were also tested, with the results 



given in Table IV. 



TABLE IV 



HARDNESS OR COEFFICIENT OF WEAR 



1 For description of this machine see the Report of the Massachusetts Highway 

 Commission for 1899, pp. 59, 60. 



